1. Technical Field
The present invention relates, in general, to a knife gate valve and, more particularly, to a multi-seal knife gate valve having improved durability and sealing capability.
2. Description of the Related Art
Generally, tubing systems requiring flow control use valves. Such valves are usually equipped with knife valves in order to control high viscosity fluid and the powders and solid granules to be carried. That is, such fluids impede the opening and shutting of a valve because of their clogging, friction, etc. and so a seat like disk is essentially used to be moved forward as if it cut the fluids, in order to open and shut the valve.
An existing knife gate valve uses a metal seat or a rubber seat according to the type of fluid and the purpose of use. However, while metal seat type knife gate valves are usually used in locations that require durability, the valves have poor sealing capability so that leakage often occurs. In the meantime, while the rubber seat type knife gate valves are used in a pipe that requires high sealing capability, the valves have poor durability to cause the problems of maintenance to occur.
That is, existing knife gate valves are of the metal seat type and the rubber seat type. However, since the metal seat type valves have excellent durability but poor sealing capability because their metal-to-metal contact structures make it difficult to maintain complete airtightness, the problems are that the valves cannot be used in pipes requiring high sealing capability. Further, while the rubber seat type knife gate valves are used in pipes requiring high sealing capability, the valves have poor durability so that there are the problems of maintenance.
The structures and problems of the existing knife gate valves that are of the type that uses the rubber seats will be described with reference to FIGS. 1 to 5.
Referring first to FIGS. 1 to 3, a first structure of the knife gate valve is a valve which is connected between pipes to open and close the flow of fluid, and which includes a valve body 10 coupled with a pipe (not shown), a disk 20 inserted into the valve body 10 so as to move vertically, and a rubber seat 30a coming into close contact with the disk 20 to maintain the airtightness.
In the knife gate valve shown in FIGS. 1 to 3, the rubber seat 30a is mounted in the inside of the valve body in such a manner as to surround the inside from the bottom up to the top of opposite sides of the inside that extend from the bottom.
While this structure can perform complete sealing, there are drawbacks of poor durability due to severe friction because when the valve is opened and closed, the rubber seat 30a comes into simultaneous contact with opposite sides of the valve disk 20. In addition, since the rubber seat 30a extends up to the upper portion of the inside of the valve body 10, there are the problems of leakage occurring at the upper portion of the valve.
Further, a seat groove is formed in the bottom of the inside of the valve body 10 to prevent the seat from being detached therefrom, so that if foreign matter gathers in the seat groove, malfunction and leakage may occur.
In the meantime, a second structure of the knife gate valve will be described with reference to FIGS. 4 and 5. This knife gate valve is also a valve that is connected between pipes to open and close the flow of fluid. The valve also includes a valve body 10 coupled with a pipe, a disk 20 inserted into the valve body 10 to move vertically, and a rubber seat 30b coming into close contact with the disk 20 to maintain airtightness. However, the shape of the rubber seat 30b is different from that of the former rubber seat.
That is, the rubber seat 30b shown in FIGS. 4 and 5 is a ring type seat including two seat parts which are inserted and assembled into a flow passage of the valve body 10 in opposite directions. That is, the type of the seat is such that the seat penetrates into and surrounds the passage of the valve from the outside.
In this case, the rubber seat 30b comes into contact with opposite major surfaces of the disk 20, so that when the valve is opened and closed, the rubber seat 30b is required to be close to the disk 20 without being detached therefrom. To this end, the rubber seat 30b is fabricated into a special form by inserting a metallic support into the rubber seat, which makes it costly and difficult to fabricate.
Further, since the rubber seat 30b comes into contact with the opposite surfaces of the disk 20, the problem of poor durability arises because of severe friction occurring when the valve is opened and closed.
Further, because of the severe friction, the valve needs a great amount of actuation torque and therefore a huge driver for the actuation of the valve, problematically increasing the cost.